A wide variety of orthotic devices are known for use in correcting body problems or supporting body structures such as broken or displaced bones, strained or stretched tendons and ligaments or post-surgical repair.
Most orthotic devices which are custom made of thermoplastic polymeric materials use flat sheets as starting materials. The flat sheets are heated and softened, draped over molds cooled and hardened, thus forming a finished part. The molds used are generally made from plaster and this requires the taking of plaster impressions from the body part such as an arm or foot region with later formation of a positive mold made from the plaster negative mold.
In some cases, the draping process can be assisted by vacuum forming, pressure forming or other common molding techniques. These products, whether or not formed directly around the body, have a disadvantage in that they produce oversized parts which must be cut to size and then finished, usually in hand operations. The cutting and finishing times can be lengthy and time-consuming.
Conventional plastics used where molds are draped, generally have too high a temperature when moldable to be applied directly to the body and formed.
More recently, in another method of making orthotic devices, low temperature polymeric materials or plastics are used. These plastic materials become malleable at a relatively low temperature as, for example, between 150.degree.-160.degree. F. and can be applied directly to the body so as to obtain the correct body shape while molding. In some cases, flat sheets of such low temperature plastic materials can be pre-cut to the amount of preliminary preparation and to reduce the amount of secondary finishing.
When complex shapes are made or the amount of forming is large, there is some difficulty. In some cases, the low temperature plastics tend to be thinned in critical areas and in an uncontrolled way. This can weaken and reduce the rigidity of the orthosis in an undesirable way.
Plastics formed by conventional techniques from sheet material also have the tendency to revert to their original shape as, for example, the flat sheet from which they are made. Sometimes a formed orthotic must be reheated and modified. Reversion to the original flat sheet often prohibits such a modification, especially if the original orthotic was trimmed. Such reversion is generally due to the processing characteristics of the plastic. For example, in sheet formation, some stretching and orientation may occur in manufacture and in some cases, if the sheet is anisotropic and subsequently cross-linked, there is a tendency to bring the material back to sheet form under certain conditions of use. Such conditions of use are usually those conditions that exceed normal general use but are present on extremely hot days. Also, should a complete, shaped orthotic be reheated for subsequent modification, it returns to its original flat shape.